In order to develop long-lived and robust power semiconductor modules, stringent thermal and electrical requirements are made specifically of the upper and lower bonding locations of the semiconductor, that is to say the top side and underside thereof. The underside of the semiconductor is usually contacted with a solder connection or else with a sintered or diffusion-soldered connection.
The top side of the semiconductor has as standard a metallization or metal layer that is optimized for the bonding process of thick aluminium wires. Despite the expansion-intensive metallization layers on the top side and underside of the semiconductor, the semiconductors are nevertheless becoming thinner and thinner in order to reduce the electrical losses. Power semiconductors having a total thickness of only approximately 70 μm are currently available on the market.
In order to increase the reliability of the top-side contacts on the chip, it is known to cohesively sinter the metal bodies directly on the wafer or to attach them and sinter them later or, during the placement process, to position and attach them on the individual chip and to sinter them later in one process step with the sintering of the chip on the substrate; cf., inter alia, DE 10 2011 115 886 A1.
Attaching the metal bodies or else attaching chips on the substrate serves for maintaining the position of the metal bodies or the chips during the further process steps. It is only with the complete-area sintering step that a fixed, complete-area cohesive connection is produced which has the desired properties of high thermal and electrical conductivity, and also high mechanical strength extending into a high temperature range.
For the attaching itself, various possibilities are known:
For example, chips are positioned on sinter paste that has not yet dried.
Also known are methods with the aid of volatile materials (e.g. alcohol) which are applied to the sinter paste and which volatilize to the greatest possible extent during sintering.
The applicant has also disclosed a method published with WO 2010/091660 A2 and referred to as “Pick & Fix”: in this case, the attaching is carried out by precompaction of the silver suspension without producing continuous sintering. However, the precompaction already leads to adhesion without impairing the later sinterability.
What is disadvantageous about the known methods is the use of different connection materials, that is to say e.g. adhesive and sinter paste or sinter paste and alcohol, which is linked to a higher, in part complex, workload and higher costs resulting from the use, application and processing of a plurality of connection materials.
In particular, the method referred to as “Pick & Fix” involves the risk of a very fine line between the complete-area precompaction (for attaching) and the incipient complete-area sintering. The process window for attaching is therefore very small and has to be complied with carefully.
Other methods for creating high-temperature and temperature-resistant connections of electronic components are known from DE 10 2009 020 733 A1, DE 102009 022 660 B3, DE 10 2012 221 396 A1 and DE 10 2014 105 462 A1.